There are two general categories of commonly used methods for protein hydrolysis: enzymatic and chemical (e.g., acid or alkali). Chemical hydrolysis can be more difficult to control and may have the potential to reduce the nutritional quality of the resulting hydrolysates. Enzymes, on the other hand, generally hydrolyze proteins under milder conditions of temperature and pH than those which are used in alkaline or acid hydrolysis, and can target specific peptide bonds. Protein hydrolysis in the food industry generally involves the use of digestive proteolytic enzymes from animals (e.g. trypsin, pepsin, chymotrypsin) and/or food-grade enzymes from plants or microorganisms (e.g., bacteria, fungi).
A protein hydrolysate is a complex mixture of peptides of different chain lengths, together with free amino acids, the fraction of peptide bonds that have been cleaved in the starter protein being known as degree of hydrolysis (DH). Protein hydrolysis can be complicated by undesired molecular interactions, such as formation of insoluble protein aggregates, or gels.
Milk proteins, and especially whey proteins, provide a significant source of biologically active peptides. Peptides having antithrombotic, antihypertensive, analgesic, and other effects have been described, and are often inactive within the parent protein and activated when released by enzymatic hydrolysis.
Trends in food production which are intended to provide protein in more bioavailable forms, include providing proteins as hydrolysates because it makes more of the biologically active peptides readily available when consumed in a protein supplement, food, beverage, etc. Another option that recently has become popular is supplementation of the normal digestive enzymes with enzyme supplements, such as those from Aspergillus species, as well as incorporating those enzyme supplements into whey protein products so that they can presumably aid in protein digestion once the protein has been consumed.
Conventional methods for enzymatic hydrolysis of proteins generally involve series of steps, generally including steps such as diluting the protein with water, heating to achieve an optimum temperature range for the enzyme(s) used, pH adjustment, an additional heating step for the purpose of deactivating the enzyme(s), and one or more steps for increasing the solids content of the hydrolysate before it is dried. For example, U.S. Pat. No. 4,482,574 (C. Lee, 13 Nov. 1984) discloses a method having the steps of “(a) adjusting the pH of an aqueous solution of a proteinaceous material in which at least 50% of the protein is soluble in water at an alkaline pH ranging from about 7 to about 10 to a pH within the range of from about 7.5 to about 10 and at least 0.5 pH units above the native pH of the solution of proteinaceous material, said solution having a temperature of less than about 30° C., the total dissolved protein content ranging from about 0.5% and about 20% by weight when determined at said pH; (b) heating the alkaline solution of step (a) to an elevated temperature within the range of from about 50° C. and about 150° C. at a rate insufficient to cause gelation of the solution; (c) cooling said heated solution to a temperature within the range of from about 30° C. to about 2° C. within 1 hour after the said solution reaches its maximum temperature level, said cooling being conducted at a rate sufficient to prevent gelation of said protein containing solution; and (d) enzymatically hydrolyzing the protein in the so treated solution to convert the protein to a hydrolyzate.”
U.S. Pat. No. 8,101,377 (M. V. Blanton et al., 24 Jan. 2012) discloses a method having the steps of “providing a solution comprising at least one dairy protein; adjusting the pH of the solution to about 10.4 or more to form a basic protein solution, cooling the basic protein solution by adjusting the temperature of the solution to about 50° F. or less; and adding a protease enzyme to the basic, cooled protein solution, wherein the protease enzyme converts at least a portion of the dairy protein to dairy protein hydrolysates having a weight average molecular weight of about 1000 to about 10,000 Daltons.”
Guo et al. (Guo, Y. et al., Optimisation of hydrolysis conditions for the production of the angiotensin-I converting enzyme (ACE) inhibitory peptides from whey protein using response surface methodology, Food Chemistry (2009) 114: 328-333) utilized a method that involved heating the protein at 65 degrees Celsius (149 degrees Fahrenheit), cooling the protein solution to the hydrolysis temperature, and adjusting the pH with 0.1 N NaOH. The pH was maintained during hydrolysis by the continuous addition of 0.1 N NaOH, and the reaction was stopped by heating the solution for 20 minutes at 80 degrees Celsius (176 degrees Fahrenheit) to deactivate the enzyme.
What are needed are new and better ways, which preferably will require fewer steps, decrease the need for the addition of compounds used for pH adjustment, and decrease added chemical, energy, and other costs, to produce protein hydrolysates. In product fields such as nutritional supplements and performance nutrition products, for example, it would also be advantageous to combine the beneficial effects of protein hydrolysates and proteolytic enzymes to further improve the bioavailability of bioactive peptides from proteins, and especially from whey proteins, which have been shown to be a significant source of such bioactive peptides.